A known electrowetting display device includes two support plates, each of which includes a substrate. A pattern of walls is arranged on one of the support plates, the pattern defining the extent of the picture elements of the display device. The area between the walls of a picture element, also known as a pixel, is called the display area, over which a display effect occurs. The display effect is created by movement of two immiscible fluids, an oil and an electrolyte, in the picture element under the influence of an electric field. When no field is applied, the oil forms a layer covering the display area of the support plate. On application of a field, the oil contracts and the electrolyte adjoins a large part of the support plate. If for example the oil is opaque, the picture element acts as a light shutter.
The walls of the picture elements are a pattern of a hydrophilic material. The area of the support plate in the display area must to a large extent be hydrophobic for a proper operation of the picture element. During manufacture of the display device the area of the support plate where the picture elements are located is made hydrophobic by including a hydrophobic layer. The walls are made on this layer by depositing a layer of wall material on the hydrophobic layer and patterning the layer of wall material using a photo-lithographic method.
To improve the adhesion between the layer of wall material and the hydrophobic layer, the hydrophobicity of the hydrophobic layer is lowered prior to applying the layer of wall material. After formation of the walls, the support plate is annealed such that the area of the hydrophobic layer between the walls regains its hydrophobicity. However, the quality of display devices made using this method is not satisfactory.
It is desirable to provide a method for making an electrowetting display device that does not have this disadvantage.